Dimethyl esters of higher dibasic acids have very expanded use as raw materials for perfumes, various polymers, plasticizers, and so forth. In particular, dimethyl brassylate, dimethyl pentadecanedioate, and dimethyl thapsate are exceedingly useful as raw materials for producing ethylene brassylate, cyclopentadecanone and the like, which are very important as musk perfumes.
Processes now practiced and those so far proposed for producing higher dibasic acids and their esters are illustrated by the following examples pertaining to brassylic acid, pentadecanedioic acid, thapsic acid, and their esters.
Brassylic acid and esters thereof are produced by oxidizing erucic acid which is contained in rapeseed oil, with ozone or permanganic acid. This method, however, involves problems such as low yields of the oxidation, formation of various compounds by the reaction, troublesome purification of the intended product, and low purity of the product.
In addition, the following processes have been proposed for synthesizing brassylic acid: a process in which diethyl malonate is reacted with methyl undecylenate to be added thereto using di-tertbutyl peroxide, and the product is then hydrolyzed [Kirkiacharian, Berdj, Bull. Soc. Chim. Fr., (5), 1797 (1971)]; a process in which ethyl 11-bromoundecanoate and ethyl cyanoacetate are reacted by heating in dimethylformamide, and the product is decarboxylated after its hydrolysis [Dudinov, A. A., Izv. Akad. Nauk, SSSR, Ser, Khim, 1974(6), 1421-1423]; a process in which 2-ethoxycarbonylcyclododecanone and sodium hydroxide are heated in diethylene glycol and the reaction mixture is then acidified (Japanese Patent Publication No. 34,406/71); and a process in which 2,2'-methylenebis(cyclohexanone) is converted into 6,6-methylenebis(6-hexanolide) by reacting with a peroxy acid in a halogenated organic solvent in the presence of an alkali carbonate, and the product is heated with pressurized hydrogen in alcohol in the presence of metallic catalyst and an acid catalyst (Japanese Patent Application Kokai No. 113,741/80). However, these processes are not always satisfactory as industrial processes because raw materials are difficult to obtain or an expensive and hazardous peroxide is necessary to the reaction.
As to pentadecanedioic acid and esters thereof, various production processes have so far been proposed. For example, there are proposed the following processes: a process in which a dioxo ester is obtained from monomethyl glutarate acid chloride and a cadmium compound prepared from .alpha., .omega.-dibromopentane, and is subjected, after saponification, to the Wolff-Kishner reduction [A. Kreuchunas, J.A.C.S., 75, 3339(1953)]; a process in which ustilic acid obtained by the hydrolysis of ustilagic acid in methanol with alkali is treated with lead tetraacetate in glacial acetic acid, and the resulting aldehyde acid is oxidized with hydrogen peroxide in an aqueous alkali solution (U.S. Pat. No. 2,717,266); a process in which diethyl undecyleneylmalonate is obtained from undecylenic acid by a known method and reacted in toluene to add hydrogen bromide, the resulting diethyl 11-bromoundecyl malonate is reacted with diethyl malonate in the presence of sodium alcoholate, and the product is hydrolyzed and decarboxylated (Japanese Patent Publication No. 10,322/57); a process in which ethyl 15,16-dihydroxylignocerate is oxidized with sodium periodate and the resulting .omega.-oxotridecane-1-carboxylic acid is oxidized with potassium permanganate in acetone (German Patent No. 1,187,600); and a process in which aleuritic acid is treated with hydrogen bromide in acetic acid, the resulting 9,10,16-tribromopalmitic acid is converted into its methyl ester, which is then treated with zinc dust in methanol, the resulting methyl .omega.-bromohexadecenoate is treated in a solution of sodium acetate in acetic acid and reduced and saponified, and the resulting .omega.-hydroxypalmitic acid is oxidized (Indian Pat. No. 65,543). However, any of these processes cannot be said to be satisfactory in industrial production since it has problems such that too many reaction steps are required, a special reagent is used, or yields are low.
As to methods for producing diesters of thapsic acid, the following processes, for example, have been proposed; a process comprising the ring-opening dimerization of cyclohexanone with Fenton's reagent in the presence of butadiene (a half-monthly magazine "Fine Chemical", No. Aug. 1, 1978, issued by C.M.C. Co., Ltd.); a process comprising an electrolytic condensation of a monoester of azelaic acid [Japanese Patent Publication No. 11,116/63; Kovsaman, E. P., Fraidlin, G. N., and Tarkkamov, G. A., (USSR), Electrosint. Monomerov, 49-73(1980)]. The former process using Fenton's reagent problems due to various products being formed and the main product not being the desired product, and cannot be said to be satisfactory in industrial production. The latter electrolytic condensation process, according to the reference cited above, is considered to have problems due to the electrolytic apparatus being complicated and the current efficiency being low, since it is described in this reference that the cell needs to be separated by an ion exchange membrane into anode and cathode compartments and the water concentration in the anolyte is 30-40% by weight. In the latter reference, there is described a polymer-like film sparingly soluble in water and in methnol which formed on the anode, became thicker with the progress of electrolysis, and was observed even with the naked eye. In any case, the process for electrolytic condensation of such monoesters of dicarboxylic acids of large number of carbon atoms, having still many problems, cannot be said to be satisfactory in industrial production.
In addition, various fermentation processes have been proposed recently for converting n-alkanes or monocarboxylic acids into dibasic acids by use of yeast. However, these fermentation processes, poor in yield, also cannot yet be said to be satisfactory as industrial processes.